Kidney stones, also known as renal calculi, develop within the kidney and are in many cases too large to pass through the ureter and urethra. The stones are composed of both organic and inorganic materials. The inorganic components comprise most of the mass of the stone and are typically rigid crystalline masses of calcium or magnesium oxalates, phosphates, or various urates. The inorganic components ar different for each particular type of stone and therefore each stone may have different characteristics depending on the composition of its inorganic component.
The organic component of the stone is called the organic matrix (or renal matrix) and often forms an intricate mesh from the surface of the stone to the center of the stone. Although the organic component often comprises a small percentage (approximately 3% to 6%) of the entire kidney stone, it forms a mesh that extends throughout the stone and can be viewed as a "backbone" of the stone. The matrix composition is essentially the same in each urinary stone and typically comprises about 64% protein, 9.6% non-amino sugar, 5% glucosamine, and 10% bond water. The remainder of the matrix composition is inorganic ash composed mainly of calcium and various phosphates.
Kidney stones must either be surgically removed or somehow reduced to fragments small enough to comfortably pass through the ureter and urethra. Various techniques have been developed in an attempt to provide a safe and effective method of eliminating kidney stones from the human body and thereby to avoid surgical removal of the stones. One such technique involves the dissolution of urinary calculi by organic or inorganic acid solutions or reagents. This technique suffers from the fact that the acid solutions or reagents can be very irritating to the patient undergoing treatment and the time frame for dissolution is often excessively long.
Presently, several non-invasive sonic methods, invasive ultrasonic methods and laser fragmentation methods to destroy kidney stones are being explored. For example, extracorporeal shock wave lithotripsy (ESWL) is of considerable current interest and involves applying focused intense acoustic impulses which produce pressure waves greater than one kbar in amplitude. These acoustic impulses are repeatedly applied to the stone until the stone is pulverized or comminuted into fragments small enough to be passed through the ureter and urethra. Unfortunately, the acoustic pulses cannot be precisely focused onto the stone and therefore portions of the healthy kidney normally receive some of the concentrated shock waves. Since the pulses often are applied up to 2000 times in a single treatment to pulverize a stone, the healthy portions of the kidney receiving the shock waves can be injured, resulting in hematuria. Furthermore, the shock-producing electrodes utilized in ESWL are expensive and have a limited useful life. Since ESWL requires extensive repetition of acoustic impulses, the electrodes frequently become exhausted and require replacement which results in considerable lithotripter equipment expense and inconvenience.
In applicant's previous U.S. patent application Ser. No. 132,413, filed Dec. 14, 1987 and now U.S. Pat. No. 4,825,851, an alternative method for comminuting kidney stones is described which comprises introducing a surface energy lowering solution into a kidney such that a stone within the kidney is exposed to the solution and the surface energy lowering solution weakens the inorganic component of the stone to be comminuted so that the stone is more easily pulverized by acoustic impulses. This method requires a specific and different surface energy lowering solution for each stone to be comminuted depending on the content of the inorganic component of the stone.
A need therefore exists for a single method of acoustically comminuting all types of kidney stones which utilizes a reduced number of acoustic impulses so as to minimize trauma to healthy tissue and reduce exhaustion of shock-producing electrodes in ESWL equipment. The technique disclosed hereinafter should overcome the deficiencies associated with current renal calculi comminution techniques.